Charger with Orthogonal PCB for Implantable Medical Device

ABSTRACT

An external charger for an implantable medical device, comprises a housing, an alternating current (AC) coil and substrate contained within the housing, and one or more electronic components mounted to the substrate. The AC coil is configured for wirelessly transmitting magnetic charging energy to the implantable medical device. The AC coil is disposed in a first plane, with the magnetic charging energy having a field directed perpendicular to the first plane. At least a portion of the substrate has a surface extending along a second plane that is substantially perpendicular to the first plane.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.11/460,955, filed Jul. 28, 2006, which is incorporated herein byreference and to which priority is claimed.

FIELD OF THE INVENTION

The present invention relates generally to chargers for implantablemedical devices, and more particularly, to external chargers for fullyimplantable medical devices, e.g., pulse generators used in a SpinalCord Stimulation (SCS) system or other type of neural stimulationsystem.

BACKGROUND

Implantable stimulation devices are devices that generate and deliverelectrical stimuli to body nerves and tissues for the therapy of variousbiological disorders, such as pacemakers to treat cardiac arrhythmia,defibrillators to treat cardiac fibrillation, cochlear stimulators totreat deafness, retinal stimulators to treat blindness, musclestimulators to produce coordinated limb movement, spinal cordstimulators to treat chronic pain, cortical and deep brain stimulatorsto treat motor and psychological disorders, and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.The present invention may find applicability in all such applications,although the description that follows will generally focus on the use ofthe invention within a spinal cord stimulation system, such as thatdisclosed in U.S. Pat. No. 6,516,227 (“the '227 patent”), issued Feb. 4,2003 in the name of inventors Paul Meadows et al., which is incorporatedherein by reference in its entirety.

Spinal cord stimulation is a well-accepted clinical method for reducingpain in certain populations of patients. A spinal cord stimulation (SCS)system typically includes an implantable pulse generator and at leastone electrode lead that carries electrodes that are arranged in adesired pattern and spacing to create an electrode array. Individualwires within the electrode lead(s) connect with each electrode in thearray. The electrode lead(s) is typically implanted along the dura ofthe spinal cord, with the electrode lead(s) exiting the spinal column,where it can generally be coupled to one or more electrode leadextensions. The electrode lead extension(s), in turn, are typicallytunneled around the torso of the patient to a subcutaneous pocket wherethe implantable medical device is implanted. Alternatively, theelectrode(s) lead may be directly coupled to the implantable pulsegenerator. For examples of other SCS systems and other stimulationsystems, see U.S. Pat. Nos. 3,646,940 and 3,822,708, which are herebyincorporated by reference in their entireties.

Of course, implantable pulse generators are active devices requiringenergy for operation. Oftentimes, it is desirable to recharge animplanted pulse generator via an external charger, so that a surgicalprocedure to replace a power depleted implantable pulse generator can beavoided. To wirelessly convey energy between the external charger andthe implanted pulse generator, the charger typically includes analternating current (AC) charging coil that supplies energy to a similarcharging coil located in or on the implantable pulse generator. Theenergy received by the charging coil located on the implantable pulsegenerator can then be used to directly power the electronic componentrycontained within the pulse generator, or can be stored in a rechargeablebattery within the pulse generator, which can then be used to power theelectronic componentry on-demand.

FIGS. 1 and 2 illustrate one example of an external charger 10 capableof wirelessly transmitting energy to an implantable pulse generator (notshown) via inductive coupling. The external charger 10 includes anelectronic substrate assembly 14 including a printed circuit board (PCB)16, and an AC charging coil (not shown) mounted to the bottom of the PCB16, and various electronic components 20, such as microprocessors,integrated circuits, capacitors, audio transducers, connectors, mountedto the top of the PCB 16. The external charger 10 further includes apower source, and in particular a battery 24, electrically coupled tothe electronic components 20 via spring terminals 26 mounted to the PCB16. The pulse generator 10 includes a case 30, which serves to house allof the afore-mentioned components in a suitable manner. The case 30comprises a bottom half 32 and a top half (not shown) that mate witheach other in a clam-shell arrangement to enclose the inner components.The external charger 10 may also include a power on/off button to allowa user to initiate a charging function, status indicators for providingvisual and/or audible signals to the user, and recharging terminals (allnot shown) to allow the battery 24 to be recharged.

As shown in FIG. 1, electrical current flowing through the AC chargingcoil induces a magnetic field in a direction perpendicular to the planein which the charging coil 18 lies. Thus, when a face of the case 30 isoriented in close proximity to an implanted device, such that the ACcharging coil 18 is parallel to a corresponding coil within theimplanted device, the magnetic field generated by the charging coil 18induces an electrical current within a corresponding coil to charge abattery within, or otherwise provide power, to the implanted device.

As can be appreciated, the size of the charger 10 is dictated, at leastin part, by the power efficiency of the AC charging coil. Due to theclose proximity between the electronic components 20 and associatedcircuit traces on the PCB 16 and the charging coil 28, the magneticfield generated by the charging coil 18 induces eddy currents on thesurface of the PCB 18 and components 20. Eddy currents are undesirablebecause they transform magnetic energy into thermal energy, therebyreducing the power efficiency of the AC charging coil, as well asundesirably heating the electronic components 20. In addition, the eddycurrents create noise within the signals generated within the electroniccomponents 20.

There, thus, remains a need to provide a more power efficient externalcharger for an implantable medical device.

SUMMARY

In accordance with the present invention, an external charger for animplantable medical device is provided. In one embodiment, theimplantable medical device is an implantable pulse generator (IPG) fordelivering stimulation energy to a patient's spinal cord for thetreatment of pain. It is noted that the present invention may be usedwith similar electrical stimulators and/or electrical sensors that maybe used as a component of numerous different types of stimulationsystems. For example, the present invention may be used as part of apacemaker, a defibrillator, a cochlear stimulator, a retinal stimulator,a stimulator configured to produce coordinated limb movement, a corticaland deep brain stimulator, or in any other neural stimulator configuredto treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.The present invention may also be used with non-electrical implantabletherapy systems, such as with drug pumps. Although the present inventionlends itself well to therapy systems, which typically includeimplantable medical devices that require a considerable amount of energyto operate, it is to be understood that the invention is not limited toits use with implantable therapy systems. Rather, the present inventionmay be used with any type of implantable medical device used to performa medical function within a patient, whether therapeutic and/ordiagnostic

The external charger comprises a housing, and an alternating (AC) coildisposed in a first plane within the housing. The AC coil is configuredfor wirelessly transmitting magnetic charging energy to the implantablemedical device. The external charger further comprises one or moreelectronic components contained within the housing. In one embodiment,the electronic component(s) perform a signal processing function. Theexternal charger may further comprise an energy source contained withinthe housing, wherein the charging energy is derived from the energysource. The external charger may optionally be incorporated into atissue implantable system having the implantable medical device. In thiscase, the implantable medical device includes a rechargeable energysource and circuitry configured for charging the energy source inresponse to wirelessly receiving the magnetic charging energy from theexternal charger.

In accordance with a first aspect of the present invention, at least oneelectronic component comprises a plurality of electronic componentsarranged along a second plane that is substantially perpendicular to thefirst plane. Although the present inventions should not be limited intheir broadest aspects, the distribution of the electronic componentswithin a plane perpendicular to the plane of the AC coil, in turn, maycause the surfaces of the electronic components to be parallel to themagnetic field generated by the AC coil, thereby minimizing the eddycurrents created on the electronic components.

In accordance with a second aspect of the present invention, theexternal charger further comprises a substrate (e.g., a printed circuitboard (PCB)) on which the electronic component(s) are mounted. At leasta portion of the substrate has a surface extending along a second planesubstantially perpendicular to the first plane in which the AC coil isdisposed. In one embodiment, the entire portion of the substrate has asurface that extends along the second plane. In one embodiment, Althoughthe present inventions should not be limited in their broadest aspects,the disposition of the substrate within a plane perpendicular to theplane of the AC coil, in turn, may cause the surface of the substrate tobe parallel to the magnetic field generated by the AC coil, therebyminimizing the eddy currents created on any metallic elements on thesubstrate, as well as the electronic component(s). In an optionalembodiment, the external charger comprises another substrate having asurface extending along a third plane substantially parallel to thefirst plane, and one or more additional electronic components mounted tothe surface of the other substrate.

In accordance with a third aspect of the present invention, at least aportion of the substrate has a surface that does not necessarily extendalong a second plane that is substantially perpendicular to the firstplane in which the AC coil is disposed. Rather, at least a portion ofthe substrate may have a surface extending along a second plane in anon-parallel relationship with the first plane, which second plane may,e.g., form an angle with the first plane equal to or greater thanforty-five degrees.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the presentinventions.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will be moreapparent from the following more particular description thereof,presented in conjunction with the following drawings. The drawingsillustrate the design and utility of embodiments of the presentinvention, in which similar elements are referred to by common referencenumerals. In order to better appreciate how the above-recited and otheradvantages of the present inventions are obtained, a more particulardescription of the present inventions briefly described above will berendered by reference to specific embodiments thereof, which areillustrated in the accompanying drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 shows a perspective of a prior art external charger for animplantable medical device;

FIG. 2 shows a top perspective view of an external charger for animplantable device constructed in accordance with one embodiment of thepresent invention;

FIG. 3 shows a bottom perspective view of the external charger of FIG.1;

FIG. 4 shows an exploded perspective view of the external charger ofFIG. 1;

FIG. 5 is a cross-section view of the external charger of FIG. 1;

FIG. 6 is a front-top perspective view of the external charger of FIG.1, particularly showing the top housing half removed;

FIG. 7 is a front-rear perspective view of the external charger of FIG.1, particularly showing the bottom housing half removed;

FIG. 8 is a front perspective view of an electronic assembly containedwithin the external charger of FIG. 1; and

FIG. 9 is a rear perspective view of the electronic assembly of FIG. 7.

DETAILED DESCRIPTION

Turning first to FIG. 2, one embodiment of an implantable system 100constructed in accordance with the present inventions will now bedescribed. The implantable system 100 generally comprises an implantablemedical device 102, such as an IPG, and an external charger 104. In theillustrated embodiment, the IPG 102 is coupled to one or more electricalstimulation leads (not shown) that can be implanted within the epiduralspace as part of a spinal cord stimulation (SCS) system for thetreatment of chronic pain.

The charger 104 is configured for transcutaneously charging the IPG 102via inductive coupling. In particular, the charger 104 provides timevarying magnetic energy, which is received by the IPG 102. Acorresponding pick-up coil (not shown) within the IPG 102 transforms themagnetic energy into an electrical current, which is used by circuitryto charge a battery (not shown) within the IPG 102.

In the illustrated embodiment, the charger 104 is a portable device thatcan be held in one hand. For example, the charger 104 may have a maximumwidth (i.e., the dimension that would span the palm of a hand) that isless than 3 inches and may be light enough so that it is comfortable andeasy to wear for an extended period of time. The charger 104 outputsenough power (e.g., 1-2 W) to charge the battery of the IPG 102 fromcomplete or near-complete discharge to end of charge in reasonableperiod of time, e.g., four hours +/− one hour. The charger 104 is alsocapable of fully charging the battery of the IPG 102 at reasonableimplant depths. For example, the charger 104 may be in charging distanceof the IPG 102 if the bottom surface of the charger 104 is separatedless than 2.5 cm from the top surface of the IPG 102 along a verticalaxis.

The charger 104 includes a power on/off button 106 for providing a meansfor alternately turning the charger 104 on and off, and an indicatorlight 108 and internal audio transducer 110 (shown in FIGS. 6 and 7) forindicating the status of the charger 104. The power button 106 may takethe form of a momentary-contact membrane dome switch for power on/off,and the indicator light 108 may take the form of a bi-colored lightemitting diode (LED). In the illustrated embodiment, the indicator light108 is integrated with the power button 106. When the charger 104 isinitially turned on, the indicator light 108 will turn green or amberand the audio transducer 110 will provide a short audible tone.

The charger 104 will then begin wirelessly transmitting magnetic energy,while searching for the IPG 102. The audio transducer 110 will providean intermittent audible sound when the charger 104 is out-of-range ormisaligned with respect to the IPG 102, and will stop providing theaudible sound when the charger 104 is in-range and aligned with respectto the IPG 102, at which point the charger 104 may be held in place overthe IPG 102 by using double-side adhesive pads or a belt. If the charger104 becomes out-of-range or misaligned with respect to the IPG 102, theaudio transducer 110 will again generate the audible signal, so that theposition of the charger 104 relative to the IPG 102 can be readjusted. Aback-telemetry link from the IPG 102 may communicate to the charger 104when the IPG battery is fully charged. If this occurs or if the chargeris fully discharged, the charger 104 may automatically shut down. Theaudio transducer 110 may generate an audible signal that indicates whenthe IPG battery is fully charged.

In the illustrated embodiment, the charger 104, itself, is rechargeable,and thus, includes a rechargeable battery 112 (shown in FIGS. 5 and 6).The audio transducer 110 may generate a tone when the battery 112 isdepleted to indicate to the user that the charger 104, itself, needs tobe recharged. In this case, the charger 104 may be placed into a cradleof a DC charger base station (not shown) until fully charged. To thisend, as shown in FIG. 3, the charger 104 includes a pair of electricalcontacts 114 for connection to corresponding electrical contacts on thecharger base station. The indicator light 108 may turn green to indicateto the user when the charger 104 has been fully charged.

Referring further to FIGS. 4-9, the inner components of the charger 104will now be described. The charger 104 generally includes an electronicassembly 116 and a housing 118 for containing the electronic assembly116. The housing 118 has a clam-shell arrangement that includes a tophalf 120 and a bottom half 122, which are suitably coupled together,e.g., using a snap-fit interference arrangement, to enclose theelectronic assembly 116 within the housing 118. The electronic assembly116 includes a vertical printed circuit board (PCB) assembly 124, ahorizontal printed circuit board (PCB) assembly 126, an alternatingcurrent (AC) charging coil 128 (best shown in FIGS. 4 and 7)(AC coil 128not shown in FIG. 5 to better illustrate other components) disposed onthe bottom surface of the horizontal PCB assembly 126, and a powersource, and in particular, the rechargeable battery 112.

The vertical PCB assembly 124 comprises control and signal processingcircuitry 130 and a printed circuit board (PCB) 132 for carrying thecircuitry 130. The horizontal PCB assembly 126 comprises additionalelectronic circuitry 134 and a printed circuit board (PCB) 136 forcarrying the circuitry 134. The PCBs 132, 136 are standard PCBs composedof a rigid, non-conductive, substrate on which conductive pathways ortraces are etched or laminated onto the substrate. Alternatively, theelectronic circuitry 130, 134 may be mounted on flex circuits, ceramicboards, wire-wrapped boards, or any other non-conductive substrate onwhich the electronic circuitry 130, 134 may be mounted in a plane.

The horizontal PCB assembly 126 is suitably mounted to the bottomhousing half 122. The bottom housing half 122 has four bosses, a centerone 138 of which extends within an aperture 142 within the center of thePCB 136 when the horizontal PCB assembly 126 is placed within the bottomhousing half 122, and the remaining three 140 (only one shown) of whichinclude threaded inserts 141 that receive respective screws 146extending through apertures 144 located on the PCB 136. The top housinghalf 120 has a boss 145 that extends within the aperture 142 within thePCB 136 opposite the center boss 138 of the bottom housing half 122, asbest shown in FIG. 5. The vertical PCB assembly 124 is mounted to thehorizontal PCB assembly 126, such that the surface of the vertical PCB132 is perpendicular to the surface of the horizontal PCB 136. As bestshown in FIG. 8, the vertical PCB assembly 124 is electrically coupledto the vertical PCB assembly 126 via angled pin blocks 148. The angledpin blocks 148 also facilitate the mechanically coupling between therespective PCBs 132, 136.

The vertical PCB 132 includes a pair of positive and negative springterminals 150 (only one shown in FIG. 6) between which the battery 112is coupled, thereby electrically coupling the battery 112 to thevertical PCB assembly 124. The rechargeable battery 112 can take theform of any battery that can be repeatedly recharged withoutsubstantially reducing the capacity of the battery, e.g., lithiumcylindrical battery. Alternatively, other types of rechargeablebatteries can be used. Alternatively, the charger 104 may not berechargeable, in which case, the power source within the charger 104,can take the form of a standard replaceable battery. In any event, thebattery 112 provides a source of electrical energy for the charging coil128, which transforms the electrical energy into the magnetic energythat inductively charges the IPG battery. The battery 112 also providesa source of energy for the electronic circuitry 130 carried by thevertical PCB 132.

The charging coil 128 may be any suitable coil capable of creating amagnetic field in response to the flow of electrical current through thecoil, but in the illustrated embodiments, takes the form of amulti-filament copper coil having a sufficient number of windings. Thecharging coil 128 may be formed by wrapping a copper wire around amandrel, and then removing the mandrel to create an air-core coil. Thecharging coil 128 is mounted to the bottom surface of the horizontal PCB136 using suitable means, such as bonding. The terminal ends of thecharging coil 128 are soldered to the horizontal PCB 132 to electricalconnect the charging coil 128 to the vertical PCB assembly 124.

The electronic circuitry 130 mounted on the vertical PCB 132 includes anamplifier for amplifying current from the battery 112, and an oscillatorfor providing alternating current to the charging coil 128, whichinduces a time varying magnetic field in a direction perpendicular tothe plane in which the coil 128 lies. The electronic circuitry 130 alsoincludes telemetry circuitry for communicating with the IPG 102 (e.g.,to determine distance between the charger 104 and the IPG 102, or toobtain battery level from IPG 102) via the AC charging coil 128, statuscircuitry for controlling the visual and audible signals emitted by thevisual indicator 108 and audio transducer 110, and temperature sensingcircuitry for sensing the temperature of the charger 104 via athermistor (not shown) to ensure that the charger 104 does not overheatand cause burns to the patient.

The electronic circuitry 130 also includes charging circuitry forcharging the battery 112 and safety circuitry for ensuring that thebattery 112 is not overcharged. To this end, the bosses 140 along thelateral sides of the charger 104 (only one lateral boss 140 shown inFIG. 5) are located opposite the electrical contacts 114, and thethreaded inserts within the bosses 140 provide an electrical connectionbetween the electrical contacts 114 and the horizontal PCB assembly 126,which is in turn, in electrical contact with the vertical PCB assembly124 via the pin blocks 148, so that the charging circuitry may receivethe recharging energy when the charger 104 is placed within the cradleof the charger base station.

The electronic circuitry 134 mounted on the horizontal PCB 136 includesa connector 152 to which the power button 106 is operably connected tovia a ribbon cable 154 (shown in FIG. 4). The electronic circuitry 134also includes the previously described audio transducer 112. Theconnector 152 and audio transducer 110 are electrically coupled to thevertical PCB assembly 124 via the respective pin blocks 148, so thatsignals can be sent between the vertical PCB assembly 124 and the poweron/off button 106, visual indicator 108, and audio transducer 110.

As can be seen, the vertical PCB 132 extends along a plane that isperpendicular to the plane in which the charging coil 128 is disposed.In this manner, the direction of the magnetic field induced by thecharging coil 128 is parallel to the plane of the vertical PCB 132,thereby reducing, if not otherwise eliminating, the creation of eddycurrents on the vertical PCB 132 and associated electronic circuitry126. As a result, the efficiency of the charging coil 128 is increased,and the noise and heat otherwise generated by the eddy currents isminimized.

In contrast, the horizontal PCB 136 extends along a plane that isparallel to the plane in which the charging coil 128 is disposed. As aresult, the direction of the magnetic field induced by the charging coil128 is perpendicular to the plane of the horizontal PCB 136 and theassociated electronic circuitry 134. While the eddy currents will beinduced on the surface of the horizontal PCB 136, the vast majority ofthe electronic components are mounted to the vertical PCB 132. Thus,because of the reduced number of electronic components and associatedelectrical traces on the horizontal PCB 136, the eddy currents inducedon the horizontal PCB 136 will be minimized. In addition, as shown inFIG. 9, the use of a vertical PCB 132 has the additional advantage ofproviding a rear surface on which the electronic circuitry 130 can bemounted. In contrast, because the charging coil 128 is mounted on therear surface of the horizontal PCB 136, there is a limited space on therear surface of the horizontal PCB 136 to mount additional electroniccircuitry. In addition, because the vertical PCB 132 is set back fromthe charging coil 128, any adverse electrical effects that theelectronic circuitry 130 on the vertical PCB 132 is further reduced.

While the charger 104 is described as having two separate and distinctPCBs; i.e., the vertical PCB 132 and the horizontal PCB 136, it shouldbe appreciated that a single PCB having a horizontal and verticalextensions on which the electronic circuitry 130 and 134 is mounted canbe used. Alternatively, a horizontal PCB 136 or horizontal extension isnot used, in which case, the charger 104 will only have a vertical PCB132 on which the electronic circuitry 130, 134 is mounted. However,because the horizontal PCB 136 provides a convenient means for properlypositioning the connector 152 relative to the power button 106, as wellas a convenient means for mounting the charging coil 128 and the entirevertical PCB assembly 124 within the bottom housing half 122, the use ofa horizontal PCB 136 or horizontal extension is preferred.

Also, while the use of a vertical PCB 132 minimizes the induction ofeddy currents thereon, a PCB that extends along a plane different from avertical plane can be used. For example, a PCB that is oriented at a 45degree angle to the plane in which the charging coil 128 is disposed canbe used to minimize the induction of eddy currents thereon. Thesignificance is that the closer the plane in which the electroniccircuitry is distributed is to being parallel to the magnetic fieldinduced by the charging coil, the less the magnitude of the eddycurrents created in the electronic circuitry and associated PCB traces.

It should also be appreciated that, although the distribution ofelectronic circuitry along a plane perpendicular to the plane in which acharging coil is disposed lends itself well to external chargers forimplantable medical devices, the same concept can be incorporated intoany implantable medical device (e.g., the IPG 102) where it is desirableto minimize or eliminate eddy currents resulting from a rechargingfunction.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. An external charger for an implantable medicaldevice, comprising: a housing; an alternating current (AC) coil disposedwithin a first plane within the housing, the AC coil configured forwirelessly transmitting magnetic charging energy to the implantablemedical device; a substrate contained within the housing, at least aportion of the first substrate having a surface extending along a secondplane in a non-parallel relationship with the first plane; and one ormore electronic components mounted to the surface of the substrate,wherein the at least a portion of the substrate is located outside ofthe coil.
 2. The external charger of claim 1, wherein the second planeforms an angle with the first plane equal to or greater than forty-fivedegrees.
 3. The external charger of claim 1, wherein the second plane isperpendicular to the first plane.
 4. The external charger of claim 1,wherein the substrate comprises a printed circuit board (PCB).
 5. Theexternal charger of claim 1, further comprising an energy sourcecontained within the housing, wherein the charging energy is derivedfrom the energy source.
 6. The external charger of claim 1, wherein theone or more electronic components perform a signal processing function.7. The external charger of claim 1, wherein the entirety of thesubstrate extends along the second plane.
 8. An external charger for animplantable medical device, comprising: a housing; an alternatingcurrent (AC) coil disposed in a first plane within the housing, the ACcoil configured for wirelessly transmitting magnetic charging energy tothe implantable medical device; and a plurality of electronic componentscontained within the housing, the plurality of components arranged alonga second plane that is substantially perpendicular to the first planewherein the at least a portion of the plurality of electronic componentsis located outside of the coil.
 9. The external charger of claim 8,further comprising an energy source contained within the housing,wherein the charging energy is derived from the energy source.
 10. Theexternal charger of claim 8, wherein the plurality of components isconfigured for performing one or more signal processing functions.